1. Field of the Invention
The present invention relates to a technique that a television set is mounted on a rotary table in a manner that it can be viewed in any direction as desired by a viewer, and more particularly, to a degaussing apparatus and method for a rotatable video display apparatus such as a television set which is rotatable in 360xc2x0 at maximum, maintaining a purity on a screen, for viewer""s convenience without causing a color contamination on the screen caused due to a variation of an earth magnetic field according to directions.
2. Description of the Background Art
As one of techniques developed to meet one of users""desire that is being changed on time basis, a rotary television set provides a convenience that a viewer can watch the TV in his or her desired direction by mounting it on a rotative table and rotating it manually or automatically. Especially, the technique is more effectively applied to a large sized television set that is attended with a difficulty in movement. And, in this respect, it is noted that the greater the rotation angle in movement of a television set is, the more effective it is.
However, as to the rotatable video display apparatus that has been developed up till now, its rotational angle is allowed only 30xc2x0 at its maximum. The reason for this is that rotation angle in more than 30xc2x0 leads to a color contamination on a screen due to a variation of the earth magnetic field, disadvantageously causing a problem in that the original color of a subject can not be reproduced.
As is known, a television set having a rotation function is readily and conveniently rotated in any direction of right side or left side by the viewer at his or her desire without necessity of moving directly the heavy-weighed TV stand.
However, as mentioned above, when the television set is rotated more than 30xc2x0, the color contamination on the screen occurs due to the magnetization phenomenon of a braun tube that is caused due to difference of the earth magnetic field.
Therefore, in order to avoid it, the conventional television set is initially designed to be rotated less than 30xc2x0. Meanwhile, however, it surely causes a degradation in view of practicality and of an inconvenience for users in a sense that it is limited in the rotation angle especially in wide area having a wide viewing range.
FIG. 1 shows a schematic degaussing circuit of a television set in accordance with a conventional art. As shown in this drawing, the degaussing circuit includes a bridge diode BD1 and a condenser C1 for rectifying and smoothing an alternating current power supply to a direct current power supply in order to meet the requirement of a system; and a degaussing circuit unit 1 for degaussing a magnetic field formed at a CRT under the control of a microcomputer when a television set is initially turned on or when a predetermined time lapses in a standby state.
The operation of the degaussing circuit will now be described
When the television set is turned on or when a predetermined time (i.e., four minutes) lapses in a standby state, a relay RY1 is driven by the microcomputer. Accordingly, a closed loop of the degaussing circuit unit 1, that is, the loop of a device coil L1, a thermister TH1 and a switch of the relay RY1 is driven so that the magnetic field formed at the CRT is degaussed.
Meanwhile, if the viewer, who moved and thus is positioned beyond the normal viewing range, rotates the television set in a desired direction more than 30xc2x0 in ON state of the television set, a color contamination occurs on the CRT due to the earth magnetic field.
As a solution to a problem of such a color contamination phenomenon, the degaussing circuit unit 1 is to be driven, but, for this purpose, the television set should be turned off and then turned on again, which causes an inconvenience for users.
In addition, in case that the television set is desired to be rotated more than 30xc2x0, it should be sequentially rotated by 30xc2x0s in order to adjust the viewing angle by the viewer, and accordingly, the degaussing circuit unit 1 is to be sequentially driven. Then, owing to the temperature characteristics of the thermister TH1, the degaussing current does not flow successively, which causes problems in that the degaussing effect is hardly obtained or the braun tube is magnetized.
Therefore, an object of the present invention is to provide a plurality of degaussing circuits that are formed in parallel and sequentially driven one by one, which are suitable to a large-sized television set having a big screen.
Another object of the present invention is to provide a degaussing circuit which is operated by a DC degaussing circuit so as to be suitable to a small-sized television set having a small screen and operable in a vertical blanking interval that is capable of preventing a transient phenomenon occurring on a screen during operation.
Still another object of the present invention is to provide a degaussing circuit of which a tint and a current amount of a degaussing coils can be directly adjusted by a user.
Yet another object of the present invention is to provide a rotary apparatus for a television set by which the television set can be rotated in 360xc2x0 while automatically preventing a color contamination occurring on a screen due to a magnetization caused by the differences of an earth magnetic field during the rotation of the braun tube, so that a viewer can view television programs conveniently and enjoyably even in a wide area having a big viewing range.
To achieve these and other advantages and in accordance with the purposed of the present invention, as embodied and broadly described herein, there is provided a sequential driving type degaussing circuit including a rotation direction and angle detector 21 for generating each pulse by using a pair of photo sensors and slits to detect a rotation angle and a rotation direction of a television set when it is rotated manually by a viewer; a microcomputer 22 for judging the direction and the angle of the television as rotated manually on the basis of a output pulse of the rotation direction and angle detector 21, judging the rotation direction and angle of the television when it is rotated automatically by a motor, and outputting a control signal to sequentially drive the degaussing circuit if it is judged that the television set was rotated more than a predetermined angle; and a degaussing circuit unit 23 for sequentially driving one by one of a plurality of degaussing circuits under the control of the microcomputer and performing a degaussing function of a CPT.
In order to attain the above object, there is also provided a direct current degaussing circuit including: a rotation direction and angle detector 31 for respectively pulses by using a pair of photo sensors and slits to detect a rotation angle and a rotation direction of a television set when it is rotated manually by a viewer; a microcomputer 32 for judging the direction and the angle of the television as rotated manually on the basis of a output pulse of the rotation direction and angle detector 21, judging the rotation direction and angle of the television when it is rotated automatically by a motor, and outputting a control signal to sequentially drive the degaussing circuit if it is judged that the television set was rotated more than a predetermined angle; a logic combining unit 33 for logically combining a degaussing control signal outputted from the microcomputer 32 and a vertical retrace line interval detect signal so that the degaussing control signal is effective only in a vertical blanking interval; and a direct current degaussing circuit unit for driving a degaussing coil by means of a direct current power supply according to charging and discharging by a condensor when it performs a degaussing function according to the output signal from the logic combining unit 33.
In order to attain the above object, there is also provided a user adjusting-type degaussing circuit including: a microcomputer 41 for outputting a pulse width modulating signal and a driving control signal of a degaussing coil when it is judged that a television set is rotated more than a predetermined angle; a degaussing direction signal output unit 42A for increasing the driving control signal outputted from the microcomputer 41 to a proper level and outputting it; a degaussing current amount control unit 42B for converting the pulse width modulating signal outputted from the microcomputer 41 to a direct current voltage and outputting it; and a degaussing unit 43 for controlling a current direction and a current amount of a degaussing coil L1 in accordance with the output signal from the degaussing direction signal output unit 42A and the output signal from the degaussing current amount control unit 42B so as to perform a degaussing function.